Engine trouble

Silversurfer · 13-07-2014, 08:21 PM

Hi everyone,

Not sure if you can shed any light on this but if you can that would be great.

I have a Carbed Yamaha f100a. I went to go out a the beginning of the season and it would tick over fine but would not rev up. Checked compression and spark all good so had the carbs cleaned by a local engineer (sonic cleaner) all put back on carbs balanced and the boat worked since Easter. put in new spark plugs and changed fuel filter.

I was out yesterday all running well, then when coming back in and slowing to 5 knots, the engine spluttered and stalled. The only way to start it was nearly full revs. As so as you drop the revs to idle it would stall. If I reved up and got it into gear in time boat would run flat out no problem. But as soon as the revs dropped it would stall again.

I have tried cleaning the jets and fuel filter but still no joy, any ideas please?

Many thanks

Stewart

Hydrostream · 13-07-2014, 11:03 PM

Bump the choke as its about to stall, if it springs back to life strip the carbs as low speed circuit is blocked.

Also try draining the carb bowls, could be water in them.

Sounds like its fuel related!

Hydrostream · 13-07-2014, 11:04 PM

Also check new fuel filter is on tight and check fuel line for air leaks.

Silversurfer · 13-07-2014, 11:07 PM

Quote:

Originally Posted by Hydrostream

Bump the choke as its about to stall, if it springs back to life strip the carbs as low speed circuit is blocked.

Also try draining the carb bowls, could be water in them.

Sounds like its fuel related!

Thanks for response, I drained the carb bowls no water, will try the choke trick and run off another tank / line in the morning.

DoubleSix · 14-07-2014, 10:10 AM

I had identical symptoms many years ago with a blue band merc 50 (yes, that long ago). Turned out to be a corroded water jacket on the baffle plate at the exhaust outlet port.

What was happening was that at tick over the exhaust pressure was not enough to overcome the water leak pressure and water was being directed through the exhaust port in to the cylinder, thus causing the poor running/misfire/stall.

if you managed to get the revs up, the exhaust outlet pressure overcame the leak pressure and the engine ran virtually normally.

The worst thing i did was to switch it off, put the boat on the trailer for a few weeks while I thought about what to do, as the water that got in to the bore seized the engine solid. Ended up having to strip the engine right down to just the block and one stuck piston (main bearings and crank removed). Knocked it out with a hammer and wooden block, it was just gummed up with salt, amazingly there was no cylinder or piston corrosion. replaced the baffle plate and it ran perfectly.